马尾松(Pinus massoniana)人工林林窗对土壤不同形态活性有机碳的影响

研究了四川盆地低山丘陵区马尾松人工林不同大小林窗对表层土壤活性有机碳(水溶性有机碳、微生物量碳、易氧化碳)含量、分配比例及碳库管理指数的影响。结果表明:(1)林窗下土壤微生物量碳含量与分配比例较林下土壤有所升高,而水溶性有机碳与易氧化碳含量及水溶性有机碳分配比例有所降低。(2)林窗大小显著影响林窗中心土壤活性有机碳含量与分配比例。随林窗面积增大,水溶性有机碳、微生物量碳与易氧化碳含量呈现较为一致的升高趋势;水溶性有机碳和微生物量碳分配比例也升高,易氧化碳分配比例先下降后升高,稳定态碳先升高后降低;总体表现为较大林窗(900—1225m2)微生物活性强,活性有机碳含量高,且有机碳库稳定性较好。(3)土壤碳库管理指数随林窗面积增大无显著变化,但与各形态活性有机碳含量及总有机碳含量显著相关,说明土壤碳库管理指数能够相对全面地反映林窗大小对土壤碳库的影响。

Effects of gap size in Pinus massoniana plantations on different soil labile organic carbon fractions

Large areas of P. massoniana plantations are often assumed to have serious ecological problems such as reduced biodiversity and soil degradation. Logging gaps are an efficient practice used to solve these problems. We investigated how the size of forest gaps in P. massoniana plantations influenced the characteristics of different soil labile organic carbon fractions and the carbon management index. Compared with those in P. massoniana plantations, the content and proportion of microbial biomass carbon increased, while the content of water-soluble organic carbon and readily oxidizable carbon, and the proportion of water-soluble organic carbon decreased in forest gaps. The size of the forest gap had significant effects on the content and proportion of labile organic carbon fractions. With the increasing size of forest gaps, the content of water-soluble organic carbon, microbial biomass carbon, and readily oxidizable carbon increased. The proportions of water-soluble organic carbon and microbial biomass carbon increased, the proportion of readily oxidizable carbon first decreased and then increased and the non-labile carbon proportion first increased and then decreased. The content and proportion of labile organic carbon and the stability of organic carbon were relatively higher in larger (900-1225 m²) gaps. The carbon management index was not significantly affected by forest gap size, which positively correlated with the content of different soil labile organic carbon fractions and soil total organic carbon. The effects of forest gap size on soil organic carbon were relatively significant in larger (900-1225 m²) forest gaps in terms of a higher stability of organic carbon and a greater amount of microbial biomass carbon and water-soluble organic carbon. This suggests that 900-1225 m² gaps might provide optimal logging gap size for the conservation of ecological functions and natural regeneration in P. massoniana plantations.